The present invention relates to an apparatus and method for the extrusion of tubing, and, more particularly, to an apparatus and method for extruding a tubing having an variable wall thickness by varying its inner dimensions.
There are, of course, many well known and established methods and apparatus used in the extrusion of tubing, particularly plastic tubing, many of which are utilized for extruding such tubing that is to be used for medical purposes, such as in the production of catheters and the like.
Typical of such extrusions include the production of multi-lumen catheters and special purpose catheters that are custom extruded for a particular medical purpose. One need, however, is for the production by the extrusion process of a catheter having a relatively constant outer dimension but where the inner dimension can be varied so that such inner dimension can be selectively designed and manufactured by the extruder to have a varying, but predetermined dimension.
In U.S. Pat. No. 5,511,965 of Batdorf et al, there is disclosed an apparatus for the production of an extruded tubing where the inner diameter is kept relatively constant but where the outer diameter can be varied. In that patent, extrudable material is forced around a mandrel having a constant diameter, thereby establishing a constant inner diameter, but the outer die aperture is varied as desired in order to vary the outer diameter between a minimum outer diameter and a maximum outer diameter as desired by the operator.
While useful for the intended purpose, the apparatus of Batdorf et al is not applicable to the production of extruded tubing where the outer dimension is held to be relatively constant while the inner dimension is selectively varied in a predetermined manner as the extruded tubing is formed.
Accordingly, it would be advantageous to have an apparatus that could produce an extruded tubing having relatively constant outer dimensions while having the ability to vary the inner dimensions as desired by the operator in order to produce a particular specialized tubing, especially manufactured for medical use, but which is certainly also applicable to non-medical uses.